1. Field of the Invention
This invention relates to an improved paper binder and in particular to an adjustable interlocking binder that can be adjusted to hold any plurality of sheets of paper, but that can be locked tightly so that the sheets are not loosely bound as with a ring binder. The components of the adjustable locking binder are preferably molded of plastic material, are interchangeable, can be provided for two or more holes in prepunched sheets, and can be readily unlocked to add more sheets of paper. Further, the shape of the locking strap is such that it will allow threading of the paper sheet onto the element without prepunching. The binder locks by means of interlocking elements or teeth in both components of the binder.
2. Description of the Prior Art
One of the most common paper binding methods in use today is a two part metal binder. The binder includes a front and back cover perforated with standard spaced holes through which a thin narrow metal insert is passed and on which, prepunched paper sheets are placed. After the cover is placed, a grooved metal front portion, with holes at extreme ends to receive the ends of the insert is added after which the metal insert ends are bent over into the groove to confine the layers. Sliding locking members, affixed to the metal front are the slid over the bent metal insert ends to hold them in place.
The obvious advantage of this method is that the binder can be repeatedly undone to add more sheets of paper, but the thickness of the folder is only that needed to contain the papers, unlike a conventional ring binder. The art likewise exhibits some distinct disadvantages. Constant use and reuse of the metal type components can cause failure through metal fatigue in the bent parts, and the sharp edges of the metal inserts cuts the bound paper causing sheets to come loose to be lost or misplaced. Constant bending of the metal inserts causes them to deform and makes it difficult to reinsert the ends through the grooved front piece. The metal components can also cut the user and commonly the sliding tabs become loose or sloppy through use and so can slide off the metal insert, allowing the folder to come apart. An additional disadvantage of the metal binder is that it requires more energy to manufacture and assemble than a comparable plastic product.
Some attempts have been made to address the disadvantages of this prior art, most notably U.S. Pat. No. 4,174,910 to McSherry et. al. The patent discloses a plurality of binding clips with a collapsed and expanded position, so that after a paper sheet is placed over the collapsed clip, it is pressed down, locking the sheet in place. The disadvantages of this are manifold. Firstly, the paper depth allowed by the clip is very limited. The invention provides for adjustable paper depths by means of additional adjustable elements, but this requires a conscious and constant effort on the part of the user, making the binder too inconvenient for constant use. Secondly, an even greater disadvantage is that when the binder elements are collapsed onto an excessive thickness of papers, the papers exert an upward pressure on the clips, so that any force put on the clips will cause them to collapse and release the papers.
Another type of binder in common usage consists of plastic strips with connecting plastic stems that are inserted through prepunched holes in the paper sheets. The strips are pressed together, engaging the connecting stems, clamping the sheets, and locking the strips tightly together. The disadvantages of this method is that the strips cannot be disconnected and reconnected to add more sheets of paper and they are limited in the number range of sheets of paper that can be bound. Still another type of plastic binder consists of a plastic sheet folded to enclose a plurality of sheets of paper and a plastic U shaped strip that slides over the folded edge of the plastic cover sheet. There are several disadvantages to this method. First, the number of sheets that can be bound is limited, and second, because the sheets of paper are held together by pressure exerted by the U shaped strip, when the strip deforms over time, it losses clamping pressure and lets the sheets fall loose.
The disadvantages of rigid ring binders are self evident when compared to the current invention. A rigid ring binder has a fixed thickness regardless of the number of sheets of paper bound, which causes the binder to occupy excessive shelf and file space. Also, ring binders are relative expensive to produce in terms of energy and mechanism complexity.